This application is based on and claims priority to Japanese Patent Application No. 11-151478 filed May 31, 1999, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates to a feedback control system for an engine. More specifically, the present invention relates to an improved feedback control system for an engine of an outboard motor.
2. Description of Related Art
In all fields of engine design, there is an increasing emphasis on obtaining more effective emission control, better fuel economy and, at the same time, continued high or higher power output. In pursuit of better fuel economy and emission control, various types of control systems have been developed in conjunction with internal combustion engines. One of the more effective types of controls is so-called xe2x80x9cfeedbackxe2x80x9d control. With this type of control, a basic air/fuel ratio is set for the engine. Adjustments are then made from the basic setting based upon the output of the sensor that senses the air/fuel ratio in the combustion chamber in order to bring the air/fuel ratio into the desired range.
Normally, the type of sensor employed for such feedback control is an oxygen (O2) sensor which outputs an electrical signal. Generally, when the output signal voltage is high, little oxygen is present in the exhaust, indicating that a combusted air/fuel charge was rich in fuel. On the other hand, when the output signal voltage is low, substantial amounts of oxygen are present in the exhaust, thus indicating that a combusted charge was rich in air.
A conventional oxygen sensor is normally associated with a wave forming circuit which manipulates the output of the sensor to indicate an xe2x80x9conxe2x80x9d signal when the voltage of the output signal exceeds a reference voltage (i.e., a signal which results when the supplied charge is rich in fuel). On the other hand, the circuit manipulates the signal to indicate that the sensor is xe2x80x9coffxe2x80x9d when the voltage of the output signal does not exceed the reference voltage (i.e., a signal which results from a supplied charge that is rich in air).
The control operates on a feedback control principle, continuously making corrections to accommodate deviations from the desired air/fuel ratio. Adjustments are made in stepped intervals until the sensor output goes to the opposite sense from its previous signal. For example, if the mixture is too rich in fuel (i.e., the sensor is xe2x80x9con,xe2x80x9d then lean adjustments are made until the mixture strength is sensed to be lean (i.e., the sensor signal turns xe2x80x9coffxe2x80x9d). Adjustments are then made back into the rich direction in order to approximately maintain the desired ratio.
Most commonly, the oxygen sensor is the type which utilizes inner and outer platinum or platinum-coated electrodes. However, the platinum acts as a catalyst, which catalyzes the exhaust. For example, oxygen remaining in the exhaust may be catalyzed with carbon monoxide at the platinum electrode interface, creating carbon dioxide. While the effects of the platinum in improving the exhaust gas emissions may be advantageous, the oxygen content of the gas being sensed can be affected to a degree which causes the sensor to provide inaccurate data, causing the associated control system to adjust the air/fuel ratio erroneously.
For example, while the actual oxygen content of the exhaust system may correspond to an air rich air/fuel charge such that the actual signal from the sensor should indicate that the sensor is xe2x80x9coff,xe2x80x9d the above-described effect may cause the sensor to indicate little oxygen is present (i.e., as if a rich fuel charge has been supplied) by an xe2x80x9conxe2x80x9d signal. In that instance, the feedback control is arranged to adjust the air/fuel ratio in the fuel rich direction in response to the xe2x80x9conxe2x80x9d signal even though the mixture is already fuel rich.
One aspect of the present invention includes the realization that some known feedback control systems have been found to inaccurately control air/fuel ratio in an internal combustion engine. In particular, it has been found that known feedback control systems do not accurately generate the desired air/fuel ratio for combustion in the combustion chambers of the associated engine. For example, it has been found that in direct-injected 2-cycle engines, the perceived oxygen concentration in the exhaust gases, and thus the voltage output of the oxygen sensor, varies according to throttle angle and engine speed when subjected to exhaust gases having the same oxygen content. Thus, it is desirable to provide a feedback control system which can compensate for errors generated by the varying output of the oxygen sensor in different operation states of the engine.
Accordingly, an outboard motor constructed in accordance with another aspect of the present invention includes an internal combustion engine having an engine body defining at least one combustion chamber. A charge former is connected to the engine and is configured to deliver fuel to the engine body to form an air/fuel mixture within the combustion chamber. A combustion condition sensor communicates with a combustion chamber and is configured to output a signal indicative of a combustion condition in the combustion chamber. A controller is configured to control operation of the charge former. The controller includes a memory having a 3-dimensional map stored therein, the 3-dimensional map includes data regarding a target output value of the combustion condition sensor as a function of a first and a second engine operation condition. The controller is configured to adjust an air/fuel ratio of the fuel and air delivered to the engine such that a value of the output signal of the combustion condition sensor is approximately the target output value.
By including a 3-dimensional map in the controller, the present invention overcomes the problems discovered in connection with the performance of combustion condition sensors. In particular, the present invention overcomes the problems stemming from the variation of the performance of an oxygen sensor with respect to different operating states of the engine. By including a 3-dimensional map which includes data regarding target output voltages of the sensor, the controller can compensate for variations in the performance of the sensor under varying engine operating states.
According to another aspect of the invention, an outboard motor includes an internal combustion engine having an engine body defining at least one combustion chamber, a charge former configured to deliver fuel to the engine body to form an air/fuel mixture within the combustion chamber, and a combustion condition sensor communicating with the combustion chamber. The combustion condition sensor is configured to output a signal indicative of a combustion condition in the combustion chamber. A controller is configured to control operation of the charge former. The controller is also configured to determine a target output value of the combustion condition sensor corresponding to a target air/fuel ratio and to adjust the target output value of the combustion condition sensor as a function of at least a first engine operation characteristic.
According to yet another aspect of the invention, a method for controlling fuel injection comprises determining a target air/fuel ratio for an internal combustion engine, detecting at least a first engine operation characteristic of an internal combustion engine, determining a target output signal of the combustion condition sensor as a function of the first engine operation characteristic and adjusting operation of the fuel injector to generate an air/fuel mixture which causes the oxygen sensor to output a signal having a value approximately equal to the target output value.
Further aspects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments which follow.